The disclosures herein relate generally to information handling systems and more particularly to a portable information handling system providing power to an external module and employing a current limit protection circuit for the external module.
As the value and use of information continue to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Portable information handling systems (IHS's) often include external modules such as CD Read, CD Read/Write, DVD Drives and floppy disk drives, for example. The external modules typically derive their power from the unregulated DC power circuitry within the IHS, thereby placing a power drain on the resources of the IHS power subsystem. It is desirable that the IHS provide protection from an over-current state by placing a limit on the amount of power which the external modules draw.
Prior information handling systems have relied on current interrupting devices such as constant current fuses to limit the amount of power to external modules and to protect the critical power levels within the IHS. This method has been shown to be inadequate do to the large variation in current drain associated with the wide variety of external modules and the associated unpredictable power usages of these external modules. In addition, the current drain associated with each external module is affected by the voltage of the supply within the IHS. The power source of the IHS may be the AC mains or a battery powered DC source. One AC source that is used for IHS power in a fixed location is an AC adapter which provides an unregulated DC source to the internal main DC unregulated power rail of the IHS. Typical DC power sources that are used for an IHS to operate in a portable mode are nickel metal hydride batteries and lithium ion batteries. When an IHS is powered by batteries, variations in voltage occur at the main DC unregulated power rail due to the variable voltage associated with DC batteries conditional upon the level of charge.
One additional problem with the above constant current fuse approach is that selecting a single current value for the current limit does not allow the IHS to function over a full range of AC adapter output DC voltages and battery DC voltages as well as the wide range of external module power requirements. The portable IHS is left vulnerable to excessive current drain by the external module and subsequent external module faults (shorts) which could potentially cause system shutdowns and data loss.
What is needed is an information handling system which is capable of supplying power to an external module while accommodating a wide range of AC adapter output DC voltages and battery DC voltages.